Methods for the manufacture of fertilizers into particles via granulating, compaction, or other techniques are well known. The resulting fertilizers often contain an undesirable level of particles fine enough to become airborne dust. This dust is produced during the manufacture, storage and transportation of the fertilizer particles from the mechanical abrasion encountered during movement of the fertilizer particles, continued chemical reactions or curing processes after the initial particle formation, the action of moisture migration through the fertilizer during storage, and/or temperature and humidity conditions during handling and storage.
Fertilizer dust can pose safety, health, and/or environmental problems. For example, inhalation of certain fertilizer dust may pose health concerns. It can also potentially contribute to the contamination of surface water ecosystems. The generation or build-up of excessive dust in manufacturing, storage, and/or transportation facilities can also be potentially explosive if ignored. Fertilizer dust can also be a concern from an economic standpoint when fertilizer dust becomes airborne as it leads to the loss of agronomic and economic value.
Attempts have been made to control or reduce dust formation of fertilizers during storage and handling. One example includes the use of oils, waxes, blends of oil and wax, and emulsions based on these products. For example, it has been suggested that petroleum based products be used to control dust from agricultural fertilizers. See, for example, Frick, “Petroleum Based DCA's to Control Fugitive Dust,” Proceedings of the Annual Meeting of the Fertilizer Industry Round Table, Series 27, pages 94-96. However there are disadvantages involved in using these treatment methods. Over time oils tend to volatilize and/or be adsorbed into the fertilizer particle, resulting in loss of or decreased effectiveness. Waxes are also ineffective and difficult to handle because they absorb into the fertilizer particle at temperatures above their melt point and do not spread or coat the fertilizer particle surface at temperatures below their melt point. In addition, both oils and waxes have limited binding properties that are essential for long term fertilizer dust control.
Other proposed dust control methods include application of other liquids such as lignosulfonate solutions, molasses solutions, urea solutions, mixtures of these solutions, other fertilizer solutions, amines, surfactants, polymers and even water. See, for example, U.S. Pat. No. 5,360,465 to Buckholtz et al. and U.S. Pat. No. 5,328,497 to Hazlett. However, due to the water present, aqueous solutions and emulsions can accelerate the formation of fertilizer dust and exacerbate the fertilizer particles caking tendencies. These treatments also tend to lose their binding properties as the solutions and emulsions dry, thereby becoming ineffective as long term dust control agents.
Some commercially available fertilizers incorporate micronutrients into the base fertilizer for enhanced agronomic benefits. One such product is the MicroEssentials® line of fertilizers that incorporate elemental sulfur into a phosphate fertilizer base composition. However, the elemental sulfur does not bond with the underlying monoammounium phosphate (MAP) based fertilizer formulation, and is thereby prone to attrition and dust formation during storage and handling of these fertilizer granules.
There remains a need for a fertilizer granule having enhanced particle integrity that is efficient and economic to manufacture, and which prevents or reduces dust formation during storage and handling of the granules.